You have to add them to the Looper with the "Add to the Looper" button. I need to think of a better UX for that. Let me know if you have ideas!

I did that, so maybe I'm just missing something but after adding them to the looper and deleting the notes to start a new layer, the old layer doesn't play anymore.

I'd suggest instead of making the loop layers and editors "siblings" ontologically, instead default on app load to have a single layer, then have the option to add more layers and switch between them - add layer then edit, instead of creating a layer and adding it to a list.

I really do like the randomization though, it actually sounded surprisingly nice. Took me a moment to realize what was happening but it's actually a seemingly simple feature that's hard to achieve in full blown DAWs.